Electric meter



S. S. GREEN ELECTR IC METER Mrch .8, 1938.

Filed March 26, 1936 .'5 Sheets-Sheet l Mmh s, 1938. s, s. GREEN 2,110,418

ELECTRIC METER mmm lnguggpnm S. S. GREEN ELECTRIC METER -Marh 8, 1938.

3 Sheets-Sheet 3 "l QQNS Patented Mar. 8, 1938 UNITED STATES PATENT OFFICE Appiication March ze', 193s, serial No. 70,951

" 17 Claims.

This invention relates to velectric watthour meters and has been illustrated as being embodied in a two-element meter. In most of its aspects it is equally suitable for single element meters,

Y and in fact one of the important advantagesof the illustrated form ,is the readiness with which y it may be converted to a single element meter.

For many years efforts have been made to produce metersy so that they would be'not only more satisfactorylin operation but also more economical in manufacture and more economical in use from the standpoint of taking up the minimum amount of Wall space. In my copending application Serial No. 33,116, I disclosed a polyphase meter Which takes up only the Wall space heretofore required by a single phase meter, while at the same time conforming to present high standards in electrical performance. covers the interference-proof disc for polyphase meters, and a novel arrangement of the major parts which is more elcient and satisfactory, especially from the manufacturing standpoint and in requiringthe minimum of Wall space. The present application is intended to cover various by using this latter feature, and involve the use 'of very high coercive permanent magnet steels. Although the metals themselves are not new, their use in kilowatt-hour meters is new and has var- A ious advantages which are peculiar to electric meters. l

The type and arrangement of damping magnets is an importantfeature of this invention, but to make its significance clear, it is necessary to briefly explain the action of damping magnets in an electric'meter. A damping magnet sets up a magnetic eld for opposing the rotation of the disc to make its speed proportional to the power vconsumptionmeasured by the meter. The disc does not touch the magnets, and in fact rotates With as little friction as possible. It is.common practice in damping magnet arrangements to provide` two adjacent fields of opposite polarity through `which the, meter disc rotates. The ldamping effect depends upon the speed of change of vilux in a given portion of the disc as it passes vthrough these elds. This speed of change depends, in turn, not only on the total magnetic. ux in these fields, but also on their concentration and proximity. The most important parts of the two elds are those parte which are adjacent to one another, since the stronger these two parts are, the more rapid will be the change yof iiuxthrough a given portion of the disc as it from one to the other.

That application' improvements, most of which are made possible (Cl. ITI-'5264) In the past, one common way of producing adjacent fields of opposed polarity and adequate strength was to provide'a large magnet having both of its poles above the disc, with an armature below the disc opposite said poles, the ilux passing downwardly from one pole into the armature and upwardly from the armature to the other pole. This was a fairly economical manner of attaining this result, but it had several drawbacks which caused 'it to be discontinued commercially.

Due to the fact that the magnets, in order to be large enough to have adequate strength, extended close to the sides of the meter case, it was impossible to mount several meters side by side in closely spaced relationship without introducing what was called an adjacency error, because large portions of the damping magnet of one meter were so close to those of another meter that there would be appreciable flux leakage between the two magnets. According to the present invention this is overcome by using a small and properly positioned magnet made of a highcoercive magnetic material instead of a large magnet `of a metal conventionally used in watthour meters, such conventional metals having relatively low coercive characteristics; This small but high-coercive magnet is placed at a position suiilcientlyf removed from the periphery of the meter case, as shown at 32 in Fig. 1, so that there is no appreciable meter adjacency error; At the same time the efficiency obtained by having two opposed fields from one magnet .is retained by having both poles on one side of the disc, as seen in Fig. 6. This is in contrast to another prior practice in which'the adjacency error due to the use of one large magnet was avoided by using two smaller magnets, one for each of the two opposed iields,v each magnet straddling the disc, having one pole above the disc and the other below, and the two magnets being alined and positioned almost end to end.

Thisconstruction, however, was more expensive, partly because of the difllculty of accurately mounting the two magnets as well as the -extra cost of fabricating two magnets, instead of one. Such a construction is alsoespecially unsatisfactory when economy of space about the disc is necessary. Nevertheless this isthe practice which has been universally followed in recent years in all meters ofthehighest quality.

The large single magnet of the discontinued prior art also failed to make the best use of the available magnetic flux, since it failed to -concentrate the iiux from the two poles in the zones adjacent one another as thoroughly as this should be done. A According to the present invention the fluxes are very concentrated in these most effective zones, as seen in Fig. 6. One methodof accomplishing this is shaping the magnet so that only the faces of the poles are adjacent to the disc, the magnet extending upwardly from these poles instead oi substantially parallel to the disc as did the large single magnets ofthe prior art mentioned. Another feature which contributes toward the same end of concentration of iiux is shaping the magnet so that its cross section adjacent its poles is less than its cross section elsewhere, especially at its central portion (the upper half of the magnete). It is obvious that except for leakage, the ux of the/entire magnet is thus concentrated in the relatively small pole pieces.

With the large prior art magnet mentioned, one factor which detracted from concentration of iiux in the most effective zones was the use of a round amature, this armature being round so that it could be turned on a screw to be screwed toward or away from the meter disc and the magnet beyond ,the disc for the purpose of adjustment. According to the present invention the armature is made generally rectangular correspending in shape to the desired zone of concentration, so that it need not have any parts drawing the magnetism away from the zone of concentration. For the purpose of adjustment, the armature may be divided, and one part of it moved parallel to the disc relative to the other part. The two parts of the armature are thus `partially separated to impede the flow of flux through the armature.

Another drawback to the magnets heretofore used in meters is their requirementfor a. substantial amount of temperature compensation, which compensation takes the form of diverting part of the iiux of the magnet from its useful channels. According to the present invention the magnets are made of a type of metal which requires relatively little temperature compensation and therefore can use a relatively greater amount of their flux for the damping eiect.

An additional objection to the magnets of the prior art is that to prevent their being permanently weakened by stray elds, as a eld from the current magnet if there should be a short circuit, it was necessary to protect the permanent` According to the present invention the magnets are, of such nature that this protection is not A necessary, a high-coercive material being used.

The objects of. the invention are not only t0 overcome the difficulties previously mentioned, ybut also 'to provide a more economical and satisfactory meter construction aside from these particular considerations. One specic object, for example, is to provide an improved form of meter adjustment which, though very economical, is exceedingly delicate and accurate and capable of utilizing substantially all of the available flux.

Other objects and .advantages of my invention will be apparent from the following description, taken with the drawings, in which:

Fig. 1 is a front sectional view of the form of meter chosen for illustration, taken approximately through the line I-I of Fig. V3, with a portion of the case broken away. g f

` Fig. 2 is aperspective view of the meter frame shown inFigl 1. i

Fig. 3 is a vertical sectional view through the suitable manner.

meter case, showing the meter element in side elevation.

Fig. 4 is a Vertical sectional view through the meter adjusting armature.

Fig. 5 is a horizontal sectional view through the character- Although this invention may' take` numerous.

forms, only one has been chosen for illustration. In this -form the meter includes any suitable meter base II and cover I2 as well as the meter mechanism mounted on said base and enclosed by said cover. 'I'he meter mechanism includes an inner driving unit having a laminated core I3 which is mounted on the base in any suitable manner, a frame I4 mounted on the core I3 of the Y inner driving unit, an outer driving unit having a laminated core I6 mounted on said frame Il, a meterdisc 2| rotatably carried by the frame, the 'damping magnets 32 and their armatures 41 and 48 forming an important part ofA this invention, and a register indicated diagrammatically at 23. The driving units may be identical with those shown in my copending application Serial No. 48,713, although the laminated coresv I3 are preferably made up of a thinner stack of laminations than was illustrated in that application. Each driving unit includes a voltage coil 24 and a current coil 26. In the preferred form the laminations are secured together partly by spacer rivets 68 which also secure attachment lugs 18 and 'I9 to the cores.

Arrangement of parts An important feature of the preferred forml of this invention is the arrangement of the driving units and permanent magnets 32 as shown, with the driving units at opposite sides of the disc and the magnets 32 between the driving units and at opposite sides of the disc axis from one another, with these damping magnets having both poles adjacent one face of the disc (by which is meant that both poles are above or both poles are below the disc) and their armatures on the opposite face of the disc and alined with their poles. This arrangement 0f parts permits securing adequate damping torque for a twoelement meter in a minimum of space, without any material adjacency error, and at exceptionally low cost. 'I'his feature of arrangement is covered in applicantfs copending application previously mentioned, and it should be borne in mind that many of the remaining features may be used without this feature.

Meter frame 'I'he desirable'arrangement with damping mag-- nets between drivingmagnets is attained largely through the use of the frame I4 which is secured to the spacer rivets 68 and 14 of core I3 in any 'I'he frame I4 is constructed as shown clearly in Fig. 2 and is cast of a nonmagnetic.v material such as aluminum. 'It includes a pair of inclined seats 3| against which the magnets 32 are secured. There may desirably be a raised boss 33 on each of these seats 3|, through which is drilled a hole suitably threaded for a screw which holds the magnet in place. 75

, loop extends around and under the meter disc' A washer36 of non-magnetic material may desirably be provided between the head of the screw andthe magnet. The seats 3I are extended upwardly and integrally connected to mounting lug 38 and to brackets 4I. The brackets 4I support the upper disc bearing as is described below.

Extending downwardly from the seat 3| is an integral extension in the form of a loop 43, which 44 and includes at its bottom portion seats 46 on which are mounted the armatures 41 and 48 as explained below. The central portion of the loop 43 forms a support for the lower bearing holder I. This bearing holder is not new with the present invention andi therefore need not be described in detail. It passes through the bearing support portion 49 and screws into the same, having an annular shoulder which seats against the bottom of the support portion 49. The bearing holder 5I preferably has a jewel bearing on which y the meter disc 44 rotates. The upper end of the shaft 52 of the meter disc is kept in the vertical position in a substantially frictionless manner by an upper bearing pin which is held in a bearing holder 54. v The preferred construction of this bearing holder is adequately illustrated in my said copending application Serial No. .48,713. y

This bearing support 54 screws into a plate 56 which is shown as secured to the brackets 4I as by suitable screws 51, though the plate may be 4an integral part of the frame I4. Y

\ Damping magnet armatures theseat 46 and screwing into the armature 41.v

It is evident that the disc 44 rotates between the magnet 32 andthe armature 41.

The armature 48 may be 'the same as the armature 41 but it is preferredA that it be in two relatively movable parts to provide for adjustment of the meter, unless other adjustment of this type is provided. It should be understood that it is common practice to adjust' meters by varying the amount of damping ux which passes through the meter disc. In the present instance this 'is accomplished by shifting that part of the armature to which the numeral 48 is applied toward or away from the other part which is designated by the number 6I. The portion 6I may be secured` to its seat 46 inthe same manner as the armature 4' I is secured to the other seat 46. The

portion 48 may slide on the seat 46 and is adjustable towards and away from the armature portion 6I by means of a screw 62 engaging both y portions of the armature. Various screw are rangementsmay be used such as having the screw threaded in one member and simply pivoted in the other member `without being longitudinally movable therein. To permit more delicate adjustment, however, the ent shown' in the segment 6I and also in the segment 48 but, due to the differential pitch, it screws to the right inthe segment-6I faster than in the segment 48, and thus draws the segment 48 towards the segment 6I.

Likewise when the screw 62 is turned in the `opposite direction, it screws to theleft in segment 6I faster than in segment 48 and hence it separates the segment 48 from the segment 6I.

This movement is limited, however, b y engagement of threads 64 with the segment .48 since the threads 64 will not t the threads in the segment 48 which engage the threads 63. It isvthus seen that the length of the unthreaded or repitch to determine the maximum amount of sepa-I ration of the two armature portions 48 and 6I.

It should be observed that the diierential` and strong. If the pitch of one thread differs from that of the other by only a hundredth or a thousandth of an inch per revolution, the armatures will be separated by only the corresponding amounts. Expressing this differently and giving a typical preferred example, if the thread 64 has a pitch of twenty-four turns to an inch, and the thread 63 has a pitch of thirty-two turns to an inch, then in one revolution oi' the screw it will move one twenty-fourth of an'inch in the block 6I, but it will/move one thirty-second of an inch in the other block 48. The net movement of the block 48 will therefore be one twenty-fourth of an inch minus one thirty-second of an inch, or, in

other words, one ninety-sixth of an'inch.

vOperation of adjustable armature The operation and effect oi the adjustable armaturegare quite simple. As the two portions are separated, the reluctance ofthe armature flux path is increased and therefore less iiux passes from themagnet through the disc to the armavture and back through the disc to the magnet than with the armature portions closer together. It follows that the damping effect is reduced. It is possible that part of the reduction in damping effect is vdue to shifting the position of the fluxy as,well as to decreasing the amount of the' flux, inasmuch as when the portion 48 is moved away from the portion 6I itis no longer directlyopposite the face of the pole of the magnet 32 and therefore the iiux` may no longer be concentrated at its most 'effective position.

Mounting of frame The frame I4 is secured at its top to the core I3 of one driving unit by means of a bracket 66 which may be secured to the 1ug`38 by a screw 6.1 and to spacer rivet 6 6, by a screw 63. The bracket 66 may desirably have a leg 1I extending beyond the spacer rivetv 68 and against the core 'I3 for further rigidity. The frame I4 is further secured to the core I3 by screws 12 which may` desirably pass through bosses 13 formed on the frame, and screw into spacer rivets 14 on the laminated core structure I3. y

Mounting of front driving unit The front driving unit is secured to the frame in a manner similar to the mounting of the inner unit, or rather it is secured to-a link secured to post 16 which is formed on the lug 38 -of frame It, and to the posts Tl formed on the looped portion of the frame i6. -The driving unit -I6 is provided with an attachment lug 'I8 through which a screw is passed and screwed into the bracket 1E. It is likewise provided with outstanding attachment lugs I9` through which screws may be passed and screwed into posts 11.

It will be observed that the two core structures` i3 and I6 are identical, even as to the lugs provided for mounting. As a mattei' of fact, spacer rivets 0l on the front core i6, similar to the spacer rivets it, may be used for mounting the register 23 and name plate 82, both of which are secured to mounting plate 83 which is secured directly to said spacer rivets.

Damping magnets higher coercive force values, are the high cobalt steels and the nickel aluminum steels. Qne form of the latter group which vhas become available commercially is known by the trade designation of Alnico because in addition to about 20% nickel and about 12% aluminum it also contains about 5% cobalt, the rest being iron. A good survey of the iield of such available materials together with a bibliography is contained in an article by C. S. Williams in the January, 1936, issue of Electrical Engineering and need not be further discussed here. Therel are numerous patents purporting to relate to high-coercive steels, including Patents Nos. 1,633,805, 1,947,274, 1,989,- 551, 1,968,569, 2,027,994, 2,027,995, 2,027,996,2- 027,997, 2,027,998, 2,027,999, and 2,028,000.

For reference, the following table of typical coercive values of different common materials is included:

not be considered as in a class with the latter two materials, since these are characterized by having a coercive force value of at least three times that of the chrome variety that of Alnico being over six times. There are, of course, steels between those mentioned above, such as 17% cobalt steel, but this table shows the dierence between low and high coercive steels.

It will be noted from thev second column that the residual flux values of the Alnico are somewhat lower than for the other materials but this is more than made up for by the highl coercive value for the material when used in accordance with this invention because the structure, gap and shaping of the magnet in this case is such as to capitalize on or take advantage of this factor .rather than to throw itv away. 'I'he last two known before the present invention.

metals are able to force much more flux through the meter disc than chrome steel or others of its class, if each were made up in a magnet of a given size.

Although various general characteristics of these metals have been known almost asV long as the metals themselves, the metals have certain advantages peculiar to kilowatt-hour meters not This is partly because all the higher coercive materials are much greater in cost on a weight basis than the commonly used chrome variety. Radical changes in mode of application to the watthour meter mechanism have been necessary to make .their use commercially possible, since high-coercive steel used along the lines of recent meter designs would have had much more total coercive force than could be used effectively, and hence much higher cost than would have been justified.

The primary change has been the use of a new magnet of short total length compared with the gap length. With the chrome steel the ratio of useful magnet length to gap length has usually exceeded 50 to 1. In the present preferred form of the invention I have found a ratio of even as low as ten to one to be sufficient. This has been the basis -for the selection of a small length magnet oi' general horse-shoe shape but of heavy cross-section in which the flux is forced through the disc gap twice, thus, in reality, doubling the actual length of gap as far as the flux path is concerned. Such extra gap length is the means by which the high coercive force of the steel is utilized. It may be noted at this pointv that if the armature is fixed with respect to the magnet,

Vas is armature 41, the available coerciveforce in a magnet may be more fully used, since it is not necessary to provide an excess to take care of adjustment. For this reason other means of adjustment than varying the, armature may be preferred. The departures in fundamental gap relations and shaping have resulted' in a damping magnet so radically different from former watthour meter practiceas to introduce entirely new space Aand arrangement problems in its application to the meter disc. The solution of these has resulted in a meter ofl great flexibility, light weight, low cost, and simplicity of assembly, together with the other advantages mentioned elsewhere.

The use of a smaller magnet permits the most advantageous positioning of these magnets, especially in that it permits their being included within the space above the disc rather than projecting outwardly beyond the disc, and thus it overcomes the'tendency to adjacency errors when two meters are located closely together.

To get the best use of a given weight of metal, the magnets are preferably shaped substantially as shown in Fig. 6, in which it is seen that thev magnet, though of general horseshoe shape, is thicker at its center top portion than at its poles. The larger cross section of the magnet near the midpoint must carry not only the useful ldamping flux which crosses the gaps,'but also the leakage iiux between the poles. Thus the crossvsection near the poles need not be as great to secure operation of the magnet at the most efficient point of substantially uniform ux densityfthroughout its length. Moreover, this taperinggof the-polesy has the additional advantage of causing the flux density at the poles to be as great as further back in the magnet and, as has been pointed-out,

this concentration of flux density at the gap' greatly increases the damping effectiveness 'of a 7| given amount of ux, especially when the concentrated flux zones of opposite direction are closely adjacent to one another. The shape of the magnet shown would give approximately uniform flux density throughout the magnet.

Referring to Fig. 6, it is seen that to the left of the line A-A the flux is all downward, and to 4the right of the line A-A the flux is all upward.

Thus as a given. portion of the disc 2"I lies under the pole S, the flux will be passing downwardly through it, but when said portion moves to lie under the pole N, the ux will be passing upwardly through it. It is this change in the direction of flux passing through a given portion of the meter disc which produces the damping eiect, and the more rapid the change is, the greater is the damping effect. In other'words, it is the intensity of flux just to the leftA of the line A--A and just to the right of the line A-A which is most important in the damping effect. Due to leakage between the poles S and N, it is not possible to get high concentration of flux exactly adjacent to the lie AA, but it is possible to concentrate the flux approximately under the faces of the poles by means of the use of the armature 41. Since greater concentration of the flux close to the line A-A produces greater damping effect, itfollows that by tapering the poles, the iiux is less spread out and is l'therefore concentrated under the poles, and hence closer to the line A-A than if `the poles, not being tapered, extended further away from the line A--A. In order to obtain a magnet having this tapered shape economically, it is preferred to use a magnetic metal which may be cast or molded to this shape. noted that the proportions shown in Fig. 6 are approximately those of an alnico magnet which has been found to be satisfactory. The outer face is shown, and is slightly'longer than the inner face on account of the slant of the magnet. If the magnet is tapered too much, its eiciency might be impaired on account of increased ux leakage. p

The use, in accordance with this invention, of the rectangular armatures 41 and 48 substantially no larger than the spread of the poles, also contributes to the concentration of flux, since if the armature extended beyond the area of desired concentration it would draw some of the flux away from this area'. As a matter of fact. it may be desirable to have the armature slightly smaller inthe direction concentric with the disc than the dimension across the pole faces of the magnet in this direction. It might also be better to have the outer opposite sides of the poles and of the armatures radialrather than parallel.

From Fig. 1 it will be observed that the magnets 32 are slightly inclined. The chief advantage of this is thaty the average spacing between adjacent magnets .of adjacent meters is greater, although the faces of the magnets are kept at the most effective position close` to the edges of the meter discs. As a matter of fact, it is preferred that the corners of the poles of the magnets extend approximately to the edge of the disc so as to obtain the greatest damping torque.

As previously stated, magnets made with the preferred metal have very little temperature error, since they have a relatively low temperature coeicient with respect to the magnetic ilux which they produce. They do have a slight temperature error, however, and the remaining parts of the meter such as the cores I3 and I6 also have very slight temperature errors. To compensate for these errors and overcome them, a tem- It should be" perature compensating clip 9| may be provided. These clips may be secured underneath the washers 36, one ,under each washer, an'd may be somewhat U-shaped if desired so as to 'extend closer to the faces of the poles of the magnet, 5 thus straddling the horizontal portion of the frame Il as do the magnets themselves. The washers 36 may be specially shaped, being attened along their lower side so as to fit above the horizontal portion of the frame I4 and, ii' 10 desired, being recessed on their inner faces to receive the clips 9i. As is Well known, these temperature compensating clips may be made of any magnetic metal having a negative temperature coefiicient such as nickel steel. One well known steel widely used for this purpose contains 29.5% nickel and approximately 69.5% iron.

Certain important advantages of mounting the damping magnets above the disc and with armatures below, have already been discussed: ,it permits avoiding adjacency error, makes a compact arrangement of parts possible, and provides adjacent opposed elds from a single magnet. 'Ihere are, however, at least two other important advantages as comparedr to using two adjacent magnets each having one pole above and one below the disc. One is obtaining the desired width of gap and the other is in the adaptability of a two-elementl meter to a single-element meter.

Resistance of damping magnets to magnetic disw turbances When meters are installed under practical conditions on the utilities supply lines to service customers, they are likely to be subjected to two classes of magnetic disturbance. In the iirst of these, a short circuit occurs on the load side of the meter (that is on the consumers side) which may cause a transient current of from one huni dred'to even one thousand or more times the 40 rated current of the meter to ow through the current `coils, (depending upon the short-circuit capacity of the supply system and the severity of the short-circuit). In the second of these classes of magnetic disturbances, the potential circuit l of the meter is subjected to a transient over-voltage of very' short duration, usually because of a surge caused iby lightning. "These lightning surges may be of allmagnitudes up to a value sufficient to burn. up the meter, but the great majority of surges are insufiicient to do this, and dissipate themselves by causing abnormally large transitory currents in the potential windings. When either one or a combination of the above two classes of abnormal surges occur, strong magnetic elds are set up around the meter coilsand their core structuresmay become completely saturated, causing strong leakage fields. These transient fields may be of the order of hundreds or even thousands of times the normal value .of the leakage fields to which the damping magnets are subjected in usual operation. These transient fields are usually produced by alternating current (and in consequence are demagnetizing.

In prior art meters, designers have always guarded against such fields by keeping the damping magnets as far away as possible from the electromagnet coils (usually on the diametrically opposite side of the meter disc). Even further than this, they have (in. the best quality of meters) always provided some form of shield vof magnetic material (usually cast iron) between the electroof the meter of lcast iron. The shielding eiect has only guarded against magnetic surge elfects partially as it is practically impossible to completely guard against a magneto-motive-force by magnetic shield means.- (Distance between the electromagnet coils (where the disturbance originates) and the permanent magnets has been an even more important factor than the shielding of the prior art.

In the present invention the damping magnets are placed in close proximity to the electromagnet coils. Moreover. the frame of the meter is'preferably of cast aluminum, and there is no room for the addition of magnetic shields (and without greater space as well, the shield could not function eiectively).V

dent that the two most important safeguardsv of the prior art are completely absent, and a commercially acceptable job in the reduced space would be impossible except for the greatly augmented use of a third safeguard.

.This third safeguard may be more easily understood by reference to Fig. 7, and especially the .left hand portion thereof. Chrome steel `has usually been magnetically aged before its application to a meter. This ageing has consisted 'in the application of a demagnetizing force (usually in the form of a magnetic eld produced by an alternating current). This force has usuallyI been one sufficient to bring the residual flux down to approximately the point X on the curve. It will be seen that this point is at the value of B and -I-I where the maximum energy product PX is produced for the chrome steel. The

maximum energy product of a magnet is the highv est product obtained by multiplying the coercive force at any point on its hysteresis curvev iFig. 7) by the flux intensity at that point. At the top of the curve the product is 0 because the coercive yf orce is 0. At the bottom of the curve the product is 0 because the flux is 0. Somewhere between there is a maximumenergy product. Of course X could be brought down still further on the curve but not much further without considerable sacrice in energy product and hence in damping eiectiveness. \With the chrome steel this demagnetizingforce applied is about fortyflve oersteds (gilberts per centimeter). Against demagnetizing forces up to but not exceeding this, the magnet would be immune.

'With Alnico, the demagnetization 'can be continued without great sacrince of damping eiliciency to the point Y where a value of about 320 oersteds is obtained (or over seven times the value with chrome steel), with approximately the maximum energy product Py. y

Of course it may not always be necessary to go to the extreme of descending on the Alnico curve to the point Y but if necessary it can be done. 'I'he result would be a magnet immune to demagnetizlng forces up to approximately 320 oersteds.

In this connection it should be noted that some of the available coercive force of the magnet is consumed in driving the useful or damping flux across the gap, but in general much of it remains to be fully available as a safeguard against demagnetizing stray elds.

Some examples may make this matter of ageing more clear. A chrome steel magnet in wide use (by the applicants company) has a developed length of six inches, a single gap of .100", and withstands from 200 to `250 ampere turns of alternating current demagnetizatlon (or knockdoyvn, as it is commonly'called) An Alnico magnet, preferred in the present in It is therefore evithat the knockdown ampere mms per unit of ariane vention, has the same damping power, has a developed length of three inches, with tWo gaps of .125" each and Withstands 250 to 300 ampere turns of alternating current knockdown. The knockdown ampere turn values per in ch of developed length for' the two are: i

Vchrome 33-42 Amico 831-100 In this example the'Almco had not been knocked down nearly to the point Y but instead was being operated at a point at about Z. .ObviouslyI if it is no t necessary to go to Y, there is some economy by operating at a point such as Z-" It can be shown by expert and detailed analysis length are a close measure of the degreev of immunity of a given magnet to demagnetizing iniiuences such as the aforementioned surges. Therefore it can be seen that the Alnico magnet,-depending upon what A. C. knockdown isy deliberately given to it,'-.can be made atleast two times as resistant as magnets of the prior art while producing almost as much ilux, even in 'a closed circuit, or three or more times as resistant while having much greater energy value.

Actual tests vhave vshown that the utilization of this third and last factor, to the necessary degree, is the most reliable way of guarding against surges. The inventor has constructed and tested a meter with spacings and arrangement according to this invention which was actually more resistant to surges than any prior art meter, notwithstanding the close spacing.

The present invention marks the rst time that damping units and driving units have ever been successfully used in close proximity and Without shields between them of magnetic material.

\ Material used in meter frame value of the use of the high coercive metal which permits the use of the frame.

For the rst timev it has been possible to get along without added clamp members or the equivalent. Now itis possible to secure the permanent magnets directly to the frame without increasing the flux leakage. 'I'he manner ofvobtaining gap accuracy is explained under the next heading.

Another advantage is the elimination of troublesome magnetic particles which always are l likely to get into the meter with any machined parts made of a magnetic metal such as the old cast iron frames. These particles could not be removed reliably in any commercially practical way, and in a meter they were especialy likely to accumulate on the poles of the magnet, thus affecting the speed of 'the disc.

Another advantage is that the frame does not` need to be painted, since it is inherently non-corrosive. AThere has always been trouble in the past with paint chipping oil? and getting in the bearings or gap as well as leaving the frame exposed to corrosion. yIn this connection it may be 2,110,418' mentioned that the Alnico magnets are also rust proof, so that paint may be omitted from them also.

The advantage in reduction of weight in the use of an aluminum frame 4(andinthe use of any frame of its skeleton nature)- is obvious.

Obtaining desired gap width tures 41 and 48' and magnets before the disc is in place. A spacer gauge is placed on each armature and the corresponding magnet 32 is slid along its seat 3| until its rests on the spacer gauge and then the screw 3l is tightened to maintainthis spacing. The gauge is then removed `and the assembly of the meter is completed.

Uonversz'on to single-element meter Another advantage of the type of magnets here used, and one which is newly attained by the present invention is that a two-element meter mechanism such as Vthe polyphase meter illustrated, may be converted to a single element meter simply by removing the front driving unit I6 and the lefthand one ofthe damping magnets 32., Perhaps more important than this from the lstandpoint of the user of meters, a single phase type can be changed into a polyphase meter by Aadding the front electromagnet element and one damping magnet, and of course changing the connections for the outside circuit according- `ly. Also, a manufacturer can make either single phase or polyphase` meters from the same stock of parts. As a matter of practice, the disc will usually be changed, since for the polyphase meter it is preferred to use an interference proof disc such as that shown in Fig'. 8 having live insulated laminations, each having ve radial slots extending from the outer edge nearly to the center of the. discs. Such discs are expensive and are not necessary in single phase meters. The advantage of havingv the other parts standard for both single phase and polyphase meters is very important nevertheless.

Torque-balanced disc lAnother novel result of the illustrated arrangement of parts is that the forces around the disc are balanced in such a way that there is no radial pull on the disc shaft when the two driving elements are measuring equal power consumptions, no matter how great the torque may be. The two driving elements act on the disc as a whole 'in exactly opposite directions (one to the right and one to the left), and the two damping magnets also act in exactly opposite directions, so

l that each set of forces is balanced except as to torque. With suitable bearing design, this saves wear on the bearings of the disc, as compared to a construction in which both the damping magnet and the driving element being on opposite sides of the disc, tend to shift the disc bodily in one direction so that the bearing has to counterrather than to limit the invention to these features, except as the prior art may require.

I claim:

1. An electric Watthour meter including a continuously rotatable disc, a, plurality of driving units acting on said disc and having approximately parallel core' structures adjacent diametrically opposed peripheral portions ofthe disc, and

an upwardly extending damping magnet located between the cores with its pole pieces adjacent one face of the disc, and an amature adjacent the other face of the disc and alined with said pole pieces, said magnet slanting from the disc` inwardly,v and said magnet being formed oi' a metal having a `coercive strength higher than one hundred eighty oersteds.

2. An electric Watthour meter mechanism includingh a disc mounted for continuous rotation about a given axis, a plurality of driving units acting on said disc and having approximately parallel core structures adjacent diametrically opposed sides of the disc, a damping magnet substantially within a cylindrical space subtended by the disc extending steeply away from the disc, and having its poles closetogether and both adl jacent the same face of the disc and spaced substantially equally from `said axis, and an armature opposite said polesv and adjacent the opposite face of said disc and constituting a low reluctance path for causing the ux to pass through d the disc in opposite directions in passing from one pole of the magnet to the other, said damping magnet being made of a magnetic material hav-- ing a coercive strength of at least 180 oersteds and being in a magnetic state corresponding to its having been previously magnetized and then subjected to a knockdown force equivalent to at least oersteds.

3. A watthour meter includinga driving unit for rotating a disc,` a suitably ysupported frame of non-magnetic metal. a disc mounted on said frame for continuous rotation, a damping magnet secured directly to 'said frame and having both poles adjacent one face of the disc for retarding the rotation of the disc, said frame extending around to the opposite face of the disc from said magnet, and an armature secured to said frame opposite said magnet but adjacent said opposite face of the disc.

4. A watthourmeter comprising a torque producing electromagnet, a disc drivenby the electromagnet andcapable of continuous rotation, anda damping magnet for said disc, said'magnet being of general horseshoe shape with its end faces comprising pole faces both of which are ad 55 jacent one face of the disc and having an armature cooperating with said pole faces adjacent the opposite face of the disc, said magnet being made of a material having a coercive force of at least oersteds and being of such size and so positioned with respect to the armature that the ratio of the length of the flux path in the coercive portion of the magnetic circuit to the combined length of the air gaps in the path through the 'air to the armature and return is less than 25 to l. v

5. A watthonr meter comprising a torque producing electromagnet, a disc driven by the electromagnet and capable of continuous rotation,

and a damping magnet for said disc, said magnet being of general horseshoe shape with its end.

oi at least 180 oersteds, and being of such size and so positioned with respect to the armature that the ratio of the length of the flux path in the 'coercive portion of the magnetic circuit to the combined length of the air gaps in the path through the air to the armature and return is less than to 1.

6. A watthour meter comprising a torque producing eiectromagnet, a disc driven by the electromagnet and capable of continuous rotation, and a damping magnet for said disc, said magnet beingA of generalhorseshoe shape with its end faces comprising pole faces both oi' which are adjacent one face of the disc and having an armature approximately coinciding in shape with the outer edges of the pole faces cooperating with.

said pole faces adjacent :the opposite face of the disc, said magnet being made of a material having a coercive force of at least 180 oersteds and being of such size and so positioned with respect to the armature that the ratio of the length of the iiux path in the coercive portion of the magnetic circuit to the combined length of the air gaps in the path through the air to the armature and return is less than 25 to 1.`

7. A watthour meter comprising a torque producing electromagnet, a disc driven by the electromagnet and capable of continuous rotation, a damping magnet for said disc, said magnet being made in general horseshoe shape with its legs'tapering toward their ends over a substantial portion ofd their length and with its end faces comprising pole faces both of which are adjacent 'one face of the disc and having an armature cooperating with said pole faces adjacent the opposite 7 face of the disc, said magnetl being made of a material having a coercive force of at least 180 oersteds, and being of such sizeand so positioned with respect to the armature that the ratio of the length of the flux path in the coercive portion of the magnetic circuit to the combined length of the air gaps in the path through the air to the armature and return is less than 25 to 1.

8. A Watthour meter comprising a torque pro-y ducing electromagnet, a disc driven by the elec- Itromagnet and capable of continuous rotation,

and a damping magnet for said disc, said magnet being of general horseshoe shape with its end faces comprising pole faces both oi' which are adjacent one face of the disc and having an armature cooperating with said pole faces adjacent the opposite face of the disc, said magnet being made of a material having `a coercive force of at least 180 oersteds, and being of such size and so positioned with respect to the armature that the ratio of the length of the flux path in the coercive portion of the magnetic circuit to the combined length of the air gaps in the path through the air to the armature and return is less than 25 to 1, and the entire magnet being located a substantial distance from the peripheral boundary of the meter case wherebyl adjacency error is substantially eliminated. i

9. A watthour meter forpolyphase measure' ments comprising a plurality of independent y torque producing electromagnets, a disc driven bythe electromagnets, capable of continuous rotation, and including a plurality of overlapping .sections substantially electrically isolated from one another and each acted upon by only one of the driving magnets at a time, damping magnet andere face of the disc, said magnet being formed of a magnetic material of coercive strength. higher than 180 oersteds and capable of operating above the point of its maximum energy product after being knocked down with a force corresponding to at least 120 oersteds.

10. A watthour meter including a base and a meter mechanism mounted on said base, said mechanism including a driving unit, a unitary frame formed'of a non-magnetic material removably secured' to said driving unit, a pair of spaced bearings carried by said frame, a disc rotatable in said bearings and positioned by said `frame to be inductively acted upon by said driving unit, and a damping magnet carried by the frame with closely spaced poles adjacent one face of said disc, said frame extending around the.

damping magnet means carried bysaidl frame on the outside thereof and including closely spaced opposed pole portions adjacent the same face of said disci; said frame extending from the inside of .said damping magnet meansr between said opposed pole portions and aroundlthe edge of said disc.

12. A watthour meter having a continuously rotatable disc, an electromagnet driving unit having current and voltage windings subject to abnormal surges, a damping magnet in close proximity to such windings and in substantially unshielded relation with respect thereto. said damping magnet being in a magnetic state corresponding to its having been previously subjected to knockdown force of at least '10 ampere turns per -fnch of developed length of the mag' net and suilicient in magnitude for the magnet to withstand, with immunity ,from permanent weakening, the magnetic surges to which it is 13. A watthour meter having a continuouslyv rotatable disc, an electromagnet driving unit having currentand voltage windings subject to abnormal surges, a damping magnet in close proximity to such windings and in substantially unshielded relation with respect thereto, said damping magnet being made of a material having a coercive strength of at least 180 oersteds and being in ,a magnetic state corresponding to its having been previously subjected to a knockdown force of at least 70 ampere turns per inch of developed length of the magnet and suiilcient in magnitude for the magnet to withstand, with immunity from permanent weakening, the ymaglnetic surges to which it is likely to be subjected in service in its environment in the meter.

14. A watthour meter having a continuously rotatable disc, and an electromagnet driving unit having current and voltage windings subject to abnormal surges, a damping magnet system in close proximity to such windings having a magnetic circuit forming an air gap through which least 180 oersteds and g5 rotatable disc,

the disc rotates and including a magnet made of a material having a coercive strength of at being in a magnetic state corresponding to its having been previously magnetized and then subjected to a knockdown force of at least '70 ampere turns per inch of developed length of. the magnet; the remainder of the magnet system having substantially no coercive strength, and the ratio of the length of the coercive portion of the magnetic circuit to the total air gap length in the magnetic circuit being less than 25 to 1.

15. A watthour meter including a continuously rotatable disc, a driving unit for rotating said 15 disc, and a damping magnet system including a damping magnet for producing opposed and adjacent concentrated iields cutting damping magnet being made from a magnetic material of coercive strength higher than one hundred eighty oersteds, and said damping magnet system being positioned between vertical planes on each side ot the meter passing through the periphery of the disc.

16. A' watthour meter including a continuously a driving unit for rotating said disc, and a U-shaped damping magnet for rethe disc, saidV loersteds, having tarding the rotation of said disc, said damping magnet being made from a magnetic material of coercive strength higher than one hundred eighty oersteds, having closely spaced poles adjacent one face of the disc and being positioned substantially between vertical planes on each side of the meter passing through the periphery of the disc, and an armature opposite said magnet, adjacent the other face of the disc and directly bridging the poles.

17. A watthour meter including a continuously rotatable disc, a driving unit for rrotating said disc, and a U-shaped damping magnet for retarding the rotation of magnet being made from a magnetic material of' coercive strength higher than one hundred eighty closely spaced poles adjacent one face of the disc and being positioned substantially between vertical planes on each side of the meter passing through the periphery of the disc, and an armature opposite said magnet, adjacent the other face of the disc and approximately coinciding in shape with the outer edges of the pole faces of the magnet.

STANLEY S. GREEN.

said disc, said damping` 

